A hybrid white organic light-emitting diode (WOLED) with an emission layer (EML) structure composed of red phosphorescent EML/green phosphorescent EML/spacer/blue fluorescent EML was demonstrated. This hybrid WOLED shows high efficiency, stable spectral emission and low efficiency roll-off at high luminance. We have attributed the significant improvement to the wide distribution of excitons and the effective control of charge carriers in EMLs by using mixed 4,4′,4″-tri(9-carbazoyl) triphenylamine (TCTA) and bis[2-(2-hydroxyphenyl)-pyridine] beryllium (Bepp2) as the host of phosphorescent EMLs as well as the spacer. The bipolar mixed TCTA:Bepp2, which was proved to be a charge carrier switch by regulating the distribution of charge carriers and then the exciton recombination zone, plays an important role in improving the efficiency, stabilizing the spectrum and reducing the efficiency roll-off at high luminous. The hybrid WOLED exhibits a current efficiency of 30.2 cd/A, a power efficiency of 32.0 lm/W and an external quantum efficiency of 13.4% at a luminance of 100 cd/m2, and keeps a current efficiency of 30.8 cd/A, a power efficiency of 27.1 lm/W and an external quantum efficiency of 13.7% at a 1000 cd/m2. The Commission Internationale de l’Eclairage (CIE) coordinates of (0.43, 0.43) and the color rendering index (CRI) of 89 remain nearly unchanged in the whole range of luminance.Graphical abstractHighlights► External quantum efficiency increases from 13.4% at 100 cd/m2 to 13.7% at 1000 cd/m2. ► The CIE (0.43, 0.43) and CRI of 89 remain nearly unchanged. ► Mixed host and spacer are the key factors in improving the performance.

We present a simple hybrid white organic light-emitting diodes (WOLED) consisting of only two layers, i.e., a hole-transporting layer and an emitting layer. The emitting layer is formed by simply co-doping a green phosphor and a red phosphor in bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp2), which acts as the blue emitter, electron-transport material, and high triplet energy host for the phosphors, i.e., a multifunctional chromophore. This simple device exhibits a maximum power and quantum efficiency of 46.8 lm W−1 and 16.5%, respectively, with a good CRI up to 90. The versatile experimental techniques are performed to gain a deep understanding of the emission mechanism. We believe that this simple design concept can provide a new avenue for achieving ultrahigh performance WOLEDs for lighting application.Graphical abstractAn ultra-simple hybrid WOLED with high efficiency (46.8 lm W-1 and 16.5%) and CRI (90) is reported. This is one of the best hybrid WOLEDs’ stories so far considering the comprehensive properties. Versatile experimental techniques are performed to gain a deep understanding of the emission mechanism. We believe that this simple design concept can provide a new avenue for achieving ultrahigh-performance hybrid WOLEDs for lighting application.Highlights► Highly efficient hybrid white organic light-emitting diode was proposed. ► The simple device consists of a hole-transporting layer and an emitting layer. ► The maximum power efficiency of 46.8 lm W−1 with CRI up to 90 was achieved. ► This concept offers a low-cost fabrication process for hybrid white device.

This paper reports a highly efficient organic light-emitting diode (OLED) with high-quality white emission that employs a deep blue-emitting beryllium complex bis(2-(2-hydroxyphenyl)-pyridine)beryllium (Bepp2) doped with a wide-bandwidth orange-emitting fluorescent dye 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4-H-pyran (DCM) through incomplete energy transfer from the blue host to the orange dopant. The two-component WOLED exhibits ideal and stable CIE coordinates (0.334 ± 0.002, 0.337 ± 0.007) with a high color rendering index equal to 79–81 upon variation in brightness from 10 to 10,000 cd m−2. As an all-fluorophore-doped white OLED, it yields very high EL efficiencies with the peak luminescence efficiency. The peak value of luminescence efficiency (LE), power efficiency (PE), and external quantum efficiency (EQE) is 14.0 ± 0.35 cd A−1, 9.2 ± 0.25 lm W−1, and 5.6 ± 0.15%, respectively.Graphical abstractResearch highlights► WOLED uses two commercial fluorescent materials as the emitting materials. ► Two-component WOLED yields stable and ideal white CIE coordinates. ► All-fluorophore-doped WOLED presents very high EL performance (LE, PE and EQE).

Efficient blue organic light-emitting diodes have been developed based on one novel fluorescent beryllium complex bis(2-(2-hydroxyphenyl)-4-methyl-pyridine)beryllium (Be(4-mpp)2). The simple double-layer device based on Be(4-mpp)2 as the EML as well as the ETL not only shows pure and stable blue emission with the CIE coordinates of (0.14, 0.09), but also presents very high EL efficiency in terms of both the peak values (5.4% for EQE and 4.2 lm W−1 for PE) and the EQE value remaining ⩾4.0% in very wide brightness range (10–10,000 cd m−2) that indicates very good operational stability. They are the highest EL efficiencies ever reported for such saturated and stable OLED (CIE: x < 0.15, y < 0.10) to the best of our knowledge.Graphical abstractEfficient blue organic light-emitting diodes have been developed based on one novel fluorescent beryllium complex bis(2-(2-hydroxyphenyl)-4-methyl-pyridine)beryllium (Be(4-mpp)2). The simple double-layer device based on Be(4-mpp)2 as the EML as well as the ETL not only shows pure and stable blue emission with the CIE coordinates of (0.14, 0.09), but also presents very high EL efficiency in terms of both the peak values (5.4% for EQE and 4.2 lm W−1 for PE) and the EQE value remaining ⩾4.0% in very wide the brightness range (10–10,000 cd m−2) that indicates very good operational stability. These values mentioned above are the highest EL efficiencies ever reported for such saturated deep-blue OLED to the best of our knowledge.Highlights► A novel fluorescent blue-emission complex Be(4-mpp)2 was developed. ► Be(4-mpp)2-based device exhibited deep-blue EL with the stable CIE (0.14, 0.09). ► The non-doped blue OLED showed very high EL efficiency of 5.4% and 4.2 lm W−1.